An electric power converting device which outputs high electric power converts a high voltage. In this case, as a device which converts DC electric power into AC electric power, a neutral-point-clamped (NPC) inverter is used. Further, as an inverter which outputs a high voltage, a single-phase NPC inverter which provides a full-bridge using two NPC legs per phase is used.
A DC link voltage of the above single-phase NPC inverter fluctuates at a frequency which is twice as a frequency of an output voltage. Further, when the single-phase NPC inverter outputs a low frequency voltage, a fluctuation width of the DC link voltage which is a voltage of the DC link capacitor between an inverter and a converter increases.
To reduce this significant fluctuation, capacity of the DC link capacitor may be increased. However, when the capacity of the DC link capacitor is increased, it is not possible to avoid that a device becomes larger and more costly.